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Here's a little insight into the sun

Alamogordo Daily NewsBy Alan Hale

Posted:
01/10/2013 10:37:11 PM MST

Here in the depths of winter, sunlight is something we don't see as often as we might like in the Sacramento Mountains. The sunlight we do see is fairly low in the southern sky and of a fairly short duration.

Fortunately, over the coming weeks the sun will gradually climb higher above the horizon in its daily trek across the sky, and will stay above the horizon for longer and longer intervals until eventually we reach summer time. Then we will likely complain about how hot the days are, as opposed to how cold the days are now.

The sun that we all know and love will continue giving us the light and heat that we need and crave for a long time but, as is true for every other facet of life, eventually things will change. Although these changes will not take place in the sun for many millions possibly billions of years from now, they will nevertheless eventually occur.

The sun obtains its energy via the process of nuclear fusion in its core, where in the extreme temperature and pressure environment that exists, hydrogen is converted into helium (plus a small amount of energy). The supply of hydrogen is finite, and eventually it will run out. When that occurs, other processes begin to take place that will cause the sun's outer atmosphere to cool down and expand outward. The sun will then become what we call a "red giant," the "red" being due to an overall reddish color caused by the sun's relatively low atmospheric temperature, and the "giant" being due to the fact that the sun will be huge perhaps enveloping the Earth and possibly even Mars.

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Over time, that extended outer atmosphere will disperse into space. What will be left of the sun will be its core: a small, planet-sized object still very hot, but shining only through its residual heat. We call such an object a "white dwarf." Over billions to trillions of years, this white dwarf will gradually cool down and fade until, many, many aeons from now, there is no heat left, and the sun becomes a cold, inert object that might be called a "black dwarf."

We can see examples of some of these "future suns" in our nighttime skies during these long, cold winter evenings. Probably the best-known example of a red giant in these winter skies is the bright star Betelgeuse, which marks the eastern "shoulder" of the constellation Orion.

Betelgeuse, which has a distinct reddish tint even to the unaided eye, is not an exact analogy of the future sun; it is in fact much more massive and, unlike the sun, will explode as a supernova at some point in the future. But it nevertheless does provide some kind of example of what our sun will look like a few billion years from now.

The first-known example of a white dwarf orbits the bright star Sirius, in the constellation Canis Major, the big dog, located southeast of Orion. Sirius is the brightest star in the entire nighttime sky and shines brilliantly in the south on these winter nights.

The white dwarf companion to Sirius betrayed its presence by causing a back-and-forth "wobble" in the motion of Sirius itself, and was first spotted directly in 1862. The bright star Procyon, which together with Betelgeuse and Sirius constitute the "winter triangle," also has a white dwarf companion which also first betrayed its presence by a "wobbling" motion and which was first directly spotted in 1896.

Perhaps the easiest white dwarf to detect with backyard telescopes can be found in the triple-star system 40 Eridani, located in the constellation Eridanus somewhat to the west of the bright star Rigel in Orion. The main star, 40 Eridani A, is somewhat similar to our sun (albeit slightly smaller), and it is orbited by a distant pair of stars, 40 Eridani B and C. The "B" star is the white dwarf, and its companion, "C" (which is the dimmer of the pair) is a low-mass "red dwarf" star (the most common type of star in our galaxy).

Incidentally, 40 Eridani A is generally considered as being the parent sun of the fictional planet Vulcan, the home world of Mr. Spock in the "Star Trek" universe.

In Vulcan's sky, the B/C pair would appear as brilliant white and red stars, respectively dimmer than the full moon, but quite a bit brighter than Venus and we can speculate and imagine how such a sight might affect the inhabitants' myths and their sciences.

As for a black dwarf we have never detected such an object, although for obvious reasons they would be difficult to discover. However, the universe itself has not been in existence long enough for even the earliest sun-like stars to have arrived in such a state, and it will probably be a long time before any stars become completely dark.Alan Hale is a professional astronomer who resides in Cloudcroft. He is involved in various space-related research and educational activities throughout New Mexico and elsewhere. His website is www.earthriseinstitute.org.